linux-kernel - Re: [PATCH v3 2/3] x86/fpu: Add a helper to prepare AMX state for low-power CPU idle

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Date:   Mon, 4 Apr 2022 17:24:06 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <linux-pm@...r.kernel.org>
CC:     <dave.hansen@...ux.intel.com>, <peterz@...radead.org>,
        <bp@...en8.de>, <rafael@...nel.org>, <ravi.v.shankar@...el.com>
Subject: Re: [PATCH v3 2/3] x86/fpu: Add a helper to prepare AMX state for
 low-power CPU idle

On 4/3/2022 9:37 AM, Thomas Gleixner wrote:
> On Thu, Mar 24 2022 at 19:22, Chang S. Bae wrote:
>> When a CPU enters an idle state, non-initialized states left in large
>> registers may be the cause of preventing deeper low-power states.
>>
>> The new helper ensures the AMX state is initialized to make the CPU
>> ready for low-power states. It will be used by the intel idle driver.
> 
> What about AVX...AVX512? Are they harmless in that regard?

I double-checked with HW folks. Yes, that's the case. Their state 
whether initialized or not does not prevent the processor from entering 
a deeper low-power state.

> 
> If so, then the first sentence above is confusing and should clearly
> spell out that it's AMX which causes that problem.

I see. Will do that.

Thanks,
Chang